Coating manufacturers have achieved significant progress in developing novel components for polyurethanes to improve coating properties, although a need remains for novel catalyst systems. The usual catalysts for forming polyurethanes are dibutyltindilaurate and tertiary amines. Dialkyl and trialkyltin derivatives, classes of the compounds to which dibutyltindilaurate belongs, have been discussed as having some issues regarding human toxicity. See, for example, Boyer, I. J., Toxicology, 1989, 55, 253 and Lytle, T. F.; Manning, C. S.; Walker, W. W.; Lytle, J. S.; Page, D. S., Appl. Organomet. Chem., 2003, 17, 653. Divalent tin compounds as disclosed herein, which do not have alkyl-tin bonds, have now been found to be suitable as catalysts for polyurethane formation.
Organometallics of the group 14 elements, particularly dibutyltin derivatives, are known to catalyze transesterification, transcarbamoylation and urethane formation. While there has been progress in development of novel components for polyurethanes to improve coating properties, a need remains for novel catalyst systems. Typical catalysts for processes including transesterification, transcarbamolylation and urethane formation are dibutyltindilaurate and tertiary amines. Dialkyl and trialkyltin derivatives, classes of the compounds to which dibutyltindilaurate belongs, have some toxicity to humans; therefore, less toxic catalysts are desired.
Jousseaume, B. et al., (“Air Activated Organotin Catalysts for Silicone Curing and Polyurethane Preparation” (1994) Organometallics 13:1034), and Bernard, J. M. et al. (U.S. Pat. No. 6,187,711) describe the use of distannanes as latent catalysts.
Co-owned and co-pending U.S. Pat. Applications (CL-3191, CL-3464 and CL-3193), all hereby incorporated by reference in their entirety, describe different classes of tin and germanium compounds useful as catalysts. (CL-3191) describes divalent tin compounds stabilized by phenoxy groups with bulky ortho-substituents. (CL-3193) describes quadrivalent tin and germanium compounds containing more than one triorganylsilyl groups connected to tin or germanium.